[#115] apemanager: Fix type getters

* Add type instance check for nil to avoid panic by
  accessing fields.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

acl/types.go

@@ -330,10 +330,18 @@ func (bt *BearerTokenBody) SetEACL(v *Table) {
 }
 
 func (t *APEOverride) GetTarget() *ape.ChainTarget {
+	if t == nil {
+		return nil
+	}
+
 	return t.target
 }
 
 func (t *APEOverride) GetChains() []*ape.Chain {
+	if t == nil {
+		return nil
+	}
+
 	return t.chains
 }